August 29, 2003

Dry Electroencephalography: Reading Brainwaves with Less Pain and Hassle

In conventional electroencephalography (EEG), scalp abrasion and use of electrolytic paste are needed to insure low-resistance between sensor and skin. By replacing this “wet” process with dry sensors, setup and cleanup time are drastically reduced. More importantly, the number and frequency of sessions are no longer limited by the amount of abrasion human scalp can tolerate. However, the unavailability of amplifiers with sufficiently low noise and high input impedance has held back the development of dry EEG sensors until the very recently. While single-sensor comparisons of wet versus dry exist, there has yet to be a multi-sensor study. Our goals are to quantitatively evaluate dry EEG sensors under multi-sensor conditions and to develop specifications for high fidelity recording.

Dowload the poster.

Posted by torque at 3:12 PM | Comments (2) | TrackBack

Electrical and magnetic readings of mental functions

Kutas, M. and Dale, A. Electrical and magnetic readings of mental functions, in Cognitive Neuroscience, M.D. Rugg (Ed.), University College Press, 1997, pp. 197-237.

Ever since Berger's (1929) discovery that brain electrical activity (electroencephalogram (EEG)) can be measured at the human scalp, it has been assumed that in these voltage fluctuations are hidden the mysteries of the workings of the human mind. While classical neurophysiologists questioned the likelihood that such "simple" fluctuations could be the key to the complexities of understanding, talking, reasoning, imagining and supposing, the past 70 years have proven otherwise. A large body of evidence has shown that electrical and magnetic activity (human or otherwise) encode information about brain states and brain processes and, by inference, about mental states and mental processes. (p. 197)

This is a nice point. At first glance, it is surprising that signals in the 10's of Hertz or less can provide meaningful information about brain processes. Individual neurons fire at a rates orders of magnitude higher, from 250-2,000 Hz [1].

The net flow of current across the neural membrane generates an electric potential in the conductive media both inside and outside the cells. It is this electric potential that forms the basis for the electrophysiological recordings made both invasively, by lowering elecrodes into the brani, and non-invasively, by placing electrodes on the scalp for EEG/ERP (Nicholson & Freeman 1975, Nunez, 1981). The same transmembrane current flows are also responsible for the magnetic fields recorded outside the head for MEG (the magnetoencephalograph). (p. 199)

This doesn't feel completely accurate. I would, instead, paint the following picture. Whenever a neuron discharges, the net electric field in the brain fluctuates because the distribution of shielded versus unshielded charges will change. Information about the new field is propagated to all charges (as well as the scalp) at nearly the speed of light. To minimize the energy of the system, free ions, i.e., those unconstrained by cell walls, then redistribute in response to the field. Kutas and Dale's statement makes it seem like this redistribution, the "flow of current", generates the electric potential at the scalp. My conjecture is that this larger flow of current will be very very slow, much slower than changes associated with billions of neurons charging and discharging. Assuming this to be true, and accepting that the local electric field can influence neuron firing rate, it is not to far fetched to consider that it is in fact the fluctuation in the electric field can encode information.

References
[1] V. Gerasimov, "Information Processing in Human Body," [Online document], 1998, [cited 10 Sept 2001].

Posted by torque at 9:25 AM | Comments (0) | TrackBack

August 28, 2003

Chief Nelson Udu

Amazing, another one! There must be a list of potential suckers being forwarded all around Africa. The funniest thing about this one is it actually has a reference number, so they can figure which letter was sent to me. The money is getting better! This time I'm up to $31,320,000.00 (Thirty-one Million, Three Hundred and Twenty thousand United States Dollars). What do you think, should I help them so that they can use their 70% to "own properties and invest in the stable economy of your country?" Fortunately, I'm rather sane today, and realize that I should probably be working on my thesis...

Dear Sir,

First I must solicit your strictest confidence in this transaction. This is by virtue of its nature as being utterly confidential and "top secret". We are top officials of the Federal Government Contract Review Panel who are interested in importation of goods into our country with funds that are presently
trapped in Nigeria. In order to commence this business, we solicit your assistance to enable us transfer into your account the said-trapped funds.

The source of the fund is as follows:During the regime of the last Military transitional government of Gen. Abdulsalami Abubakar, government officials set up companies and awarded themselves contracts which were grossly over invoiced in various ministries. The present democratic government of President Olusegun Obasanjo set up the Contract Review Panel and we have identified a lot of inflated contract funds that are presently floating in the Central Bank of Nigeria ready for payment. However, by virtue of our positions as civil servants and members of this panel, we cannot acquire this money in our names.My colleagues in the panel have therefore delegated me as a matter of trust, to look for an oversea partner into whose account we would transfer the sum of US$31,320,000.00 (Thirty-one Million, Three Hundred and Twenty thousand United States Dollars) which we hope to use in purchasing Agro Allied Equipment, and also to enable us to own properties and invest in the stable economy of your country. Hence, we are sending you this email message.

We have agreed to share the money thus:
1. 20% for the account owner (you)
2. 70% for us (the officials of the CRP)
3. 10% to be used in settling taxation and all local and foreign expenses.

Please acknowledge receipt of this message for proper briefing on the safe modality for the execution of this project. I await your eager response.

Yours faithfully,

Chief Nelson Udu.

Please Quote this Reference number (NU/08/03) in your response.


You can learn more about Chief Udu in thefinkfile. If you really feel like you need to respond to this sort of thing, you can find a HUGE pile of them here. Eat your heart of, there must be billions of unclaimed dollars ready for the taking. Hey wait a second, Chief, who is Dr. Edward Brume? Hmmm, hey Chief, do you think you could send it to my PayPal account? Oh, drats, the maximum amount for individual transactions is $10,000.

Here are some interesting things about the message, the response address is nelson_11@epatra.com. Epatra.com is an Indian language free email service. The IP address of the mailing though, is 217.78.75.128, registered in Amsterdam, but actually in Nigeria according to GeoIP!!

Update

I snagged a 20-day trial version of Magic NetTrace, and got the following information:
% This is the RIPE Whois server.
% The objects are in RPSL format.
%
% Rights restricted by copyright.
% See http://www.ripe.net/ripencc/pub-services/db/copyright.html

inetnum: 217.78.64.0 - 217.78.79.255
netname: NG-SIOTEL-20001206
descr: SIOTEL NIGERIA LIMITED
descr: PROVIDER
country: NG
admin-c: SN1917-ORG
tech-c: SA4434-RIPE
status: ALLOCATED PA
changed: hostmaster@ripe.net 20001207
source: RIPE
mnt-by: RIPE-NCC-HM-MNT
changed: hostmaster@ripe.net 20010508
changed: hostmaster@ripe.net 20010517
changed: hostmaster@ripe.net 20020913

person: George Opara
address: #5A Karimu Kotun St.
address: Victoria Island
address: Lagos, Nigeria
phone: +234-1-3201260
phone: +234-1-3201261
phone: +234-1-3201262
phone: +234-1-3201263
phone: +234-1-3201106
fax-no: +234-1-3201268
e-mail: george@siotel.net
e-mail: gopara@mailcity.com
nic-hdl: SN1917-ORG
changed: shaibu@siotel.net 20000929
source: RIPE

person: Shaibu Ali
address: #5A Karimu Kotun St.
address: Victoria Island
address: Lagos, Nigeria=20
phone: +234-1-3201260
phone: +234-1-3201261
phone: +234-1-3201262
phone: +234-1-3201263
phone: +234-1-3201106
fax-no: +234-1-3201268
e-mail: shaibu_ali@yahoo.com
nic-hdl: SA4434-RIPE
changed: shaibu@siotel.net 20000929
source: RIPE

Posted by torque at 4:22 PM | Comments (7) | TrackBack

Brain wave recogntion publications

Patrick Suppes and Bing Han
Brain-wave representation of words by superposition of a few sine waves
PNAS 2000 97: 8738-8743.

Patrick Suppes, Bing Han, Julie Epelboim, and Zhong-Lin Lu
Invariance of brain-wave representations of simple visual images and their names
PNAS 1999; 96: 14658-14663.

Patrick Suppes, Bing Han, Julie Epelboim, and Zhong-Lin Lu
Invariance between subjects of brain wave representations of language
PNAS 1999; 96: 12953-12958.

Patrick Suppes, Bing Han, and Zhong-Lin Lu
Brain-wave recognition of sentences
PNAS 1998; 95: 15861-15866.

Patrick Suppes, Zhong-Lin Lu, and Bing Han
Brain wave recognition of words
PNAS 1997; 94: 14965-14969.

Posted by torque at 3:37 PM | Comments (0) | TrackBack

Ebay search continued...

I gained some more insight this morning. I thought at first that it should not be the Javascript cookie, since deleting did not change the behavior. However, I noticed something interesting, at the highest security settings for IE, (1) the main eBay page does not drop a cookie, and (2) the dSI function never appears. So, it must have something to do with the myriad of Javascript functions the main page is running.

Posted by torque at 11:10 AM | Comments (1) | TrackBack

August 27, 2003

Automating eBay search

Try this. Open up a browser window and jump to http://www.ebay.com. Now, in the same browser window, paste in http://search.ebay.com/search/search.dll?MfcISAPICommand=GetResult&query=donuts. Select View->Source, and do a Find for "dSI". You'll see something interesting:

dSI(0,1,0,0,1,0,0,1,0,0,0,2,2341979206,"*L@@K*-100*Dog*CHEWS & RAWHIDE BONES *Donuts",20753,'','$2.99','','$12.98',1,"1m","0h 01m","in 1 min","Aug-27","16:29","Aug-20","16:29",{});
This is very interesting, because it gives information, in an easily parsable form, on each item on the page. You might think to yourself, what a great way to parse eBay searches. However, all is not so straight-forward. First of all, if you open a new window and just paste in http://search.ebay.com/search/search.dll?MfcISAPICommand=GetResult&query=donuts and do a search for "dSI" in the source, you won't find it. Something happens when you first enter the eBay home page. It isn't a header cookie, and I'm not sure it is the one put in by Javascript. It may have something to do with the eTag header. It is known that Java servlets use this field to run sessions. I tried cURL with cookies to no avail. Anyone have any ideas?

dSI is a function found in the included sale_search.js file. Kindly, eBay gives definitions to all the fields:

  • featured
  • galleryType
  • giftIconType
  • siteId
  • saleType
  • IsHighlightSearch
  • IsBoldSearch
  • IsPicturePackItem
  • IsNewItem
  • IsHomesDirect
  • IsSothebys
  • offerCount
  • ItemId
  • ItemTitle
  • CatId
  • ConvertedPriceMoneyStandard
  • CurrentPriceMoneyStandard
  • ConvertedBinPriceMoneyStandard
  • BinPriceMoneyStandard
  • IsTimeInMinutes
  • TimeLeftInMinutes
  • TimeLeft
  • TimeInMinutes
  • EndTimeDateMedium
  • EndTimeTimeLong
  • StartTimeDateMedium
  • StartTimeTimeLong
  • Attr
I became interested in this after puzzling over the now non-functioning ebayrss, which was developed to avoid the somewhat pricy eBay API fees.

Posted by torque at 4:39 PM | Comments (178) | TrackBack

August 25, 2003

Could it be a... scam?

I received this suspicious mailing this afternoon... what do you think? Anyone else get this? It's nice that they are so nice to inform you ahead of time that they are keeping 70% for themselves... A common way that these things manifest themselves, though for smaller amounts, is that someone in Africa will offer to buy something from you. They will send too much money, and then, after you've deposited the money, ask for you to send back some of the money. Well, guess what, after you send the money you'll find out that the check is bad... sorry, you lose. So... be careful. This can happen with bikes, horses, or even boer goats! After reading it check out a special mailing from Alex Moroka... sound familiar? Seriously, here's what you SHOULD do if you get one of these.

X-Message-Info: 6sSXyD95QpUUyx1lS9BGBYqXmoycg6uv Received: from web20709.mail.yahoo.com ([216.136.226.182]) by mc7-f17.law1.hotmail.com with Microsoft SMTPSVC(5.0.2195.5600); Mon, 25 Aug 2003 15:38:42 -0700 Message-ID: <20030825223839.64466.qmail@web20709.mail.yahoo.com> Received: from [62.56.191.150] by web20709.mail.yahoo.com via HTTP; Mon, 25 Aug 2003 23:38:39 BST Date: Mon, 25 Aug 2003 23:38:39 +0100 (BST) From: "=?iso-8859-1?q?Dr.Tony=20Williams?=" Subject: STRICTLY CONFINDENTIAL: To: _______________ MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-Path: drtonywilliams4@yahoo.ie X-OriginalArrivalTime: 25 Aug 2003 22:38:42.0642 (UTC) FILETIME=[A2F03B20:01C36B59]

From:Office of the director,
AUDTING AND ACCOUNT UNIT.
BANQUE INTERNATIONAL AFRIQUE
DE L' OUEST,LOME,REPUBLIC
OF TOGO.

Dear ____________,

I am privileged to write you through the Internet as
the DIRECTOR OF AUDITING at the account section of
BANQUE INTERNATIONAL AFRIQUE DE L'OUEST here in LOME
REPUBLIC DU TOGO (B.I.A).

Our late Customer, a national of Your Country who died
along with his wife and his Two sons in an auto crash
accident along Sagwamah express road LOME over 3 years
now was an astute businessman, an oil merchant and
contractor here in TOGO and he left behind a deposit
of Eight Million,Two Hundred Thousand United States
Dollars only($8,200,000.00usd) in his domiciliary bank
account in above mentioned BANQUE INTERNATIONAL
AFRIQUE .

Efforts made by the Bank to get in touch with of any
of his relatives proves no success and due to the
perceived possibilities of not being able to locate
any of his relatives or business associates( since no
record of any relatives is known to us) made the
management of this bank under the influence of our
Chairman and some members of the Board of Directors,
to have series of meetings and decided to declared the
fund 'unclaimed' and subsequently send it to the
Government Suspense Account for funding of the
purchase of arms and ammunition to further enhance the
course of War in Africa.

In order to avert this negative development, I on
behalf of my trusted colleagues now seek your
permission to have you stand in as next of kin to Our
late Customer so that the fund will be released and
paid into your account as the beneficiary's next of
kin now that the bank is still expecting a next of kin
or relative of the deceased. Infact we could have done
this deal alone but because of our position in this
country as civil servants, we are not allowed to
operate a foreign account and that would eventually
raise an eye brow on our side during the time of
transfer since we still work in this bank, this is the
actual reason why we required a second party or fellow
who will assist us forward claims as the next of kin
and also provide either an existing bank account or to
set up a new Bank a/c immediately to receive this
fund, even an empty a/c can also serve for this
purpose.


Note that all needed documents to enable the fund get
to your account will be carefully worked out and
meanwhile,all the whole arrangement to put claim over
this fund as the bonafide next of kin to the deceased
and to get the required approval and transfer this
money to a foreign account has been put in place and
all necessary information will be disclose to you as
soon as you indicate your interest and willingness to
assist us.

On smooth conclusion of this transaction,you will be
entitled to 25% as gratification for your assisting
us, while 5%will be set aside to take care of expenses
on our both sides that may arise during the time of
transfer and also for telephone bills, and the
remaining 70% will be for me and my partners.

Meanwhile we will be monitoring the whole situation
here in this bank until the money is confirmed into
your account and we shall come down to your country or
any nominate place for us to meet for subsequent
sharing of the fund accordingly as indicated above and
further investment, either in your country or any
country you advice us to invest in. All other
necessary information will be send to you when we hear
from you.

Bear in mind that this proposal is 100% risk free.

I suggest you get back to me as soon as possible
stating your wish in this business Via
twilly1@zwallet.com

Yours faithfully,

Dr Tony Williams.
+228-903-7431.

Posted by torque at 3:49 PM | Comments (48) | TrackBack

August 23, 2003

Paul Baloche

He wrote "Above All", a song we'll be singing tomorrow AND he has an online songbook available for free. What a nice guy! How did he swing this with his publishers? God bless him.

Posted by torque at 10:35 PM | Comments (1) | TrackBack

Salad buffet bonanza

After so many years, Fresh Choice remains high up in my favorite restaurants. Souplantation and Sweet Tomatoes are good too. All of them are clean, kid-friendly, and serve unlimited good food. What more could you ask for? In case you decide to go, make sure you print out the coupons from the website. Here's the August coupon:

Posted by torque at 10:03 PM | Comments (0) | TrackBack

Vineyard Music

Preparing for worship practice tomorrow (err, today), I stumbled on an excellent resource, Vineyard Music. I especially appreciated the free mp3's and the audio clips of Tim Hughes. This week we'll be singing "Above All" by Lenny Leblanc and Paul Baloche. Great lyrics.

Posted by torque at 2:08 AM | Comments (0) | TrackBack

August 22, 2003

Nice photos!

Messing around, I found another Tim's Journal with some very incredible photos. I'm jealous! Take a look at the three botanical garden blogs.


The main photo gallery is here. Very impressive work.

Posted by torque at 5:14 PM | Comments (2) | TrackBack

Chloroplast Movement

I've always wondered about this. Here are the little guys going around in circles. Why? Anyone know?

Posted by torque at 1:42 PM | Comments (1) | TrackBack

August 21, 2003

The Lord's mercy

'And I will bring Israel back to his pasture and he will graze on Carmel and Bashan, and his desire will be satisfied in the hill country of Ephraim and Gilead. In those days and at that time,' declares the LORD, 'search will be made for the iniquity of Israel, but there will be none; and for the sins of Judah, but they will not be found; for I will pardon those whom I leave as a remnant.' - Jer 50:19-20

Those days refers to the days that the king of Babylon and his land are punished (vs. 18). Does that mean that this has already happened? Who are the remnant? What a blessing to be pardoned.

Posted by torque at 8:05 AM | Comments (0) | TrackBack

August 20, 2003

An overview of Babak's dry EEG sensor

In mid-90s, Alizadeh-Taheri et al. produced an insulated electrode designed specifically for EEG and built using conventional semiconductor fabrication equipment [1].  Several interesting features were incorporated including multiple electrode contacts for redundancy, electrostatic discharge (ESD) circuitry, and an application-specific ultra-low noise amplifier.  Silicon nitride (Si3N4) was selected from materials common to thin-film capacitors as the insulating material because of its excellent resistance to chloride corrosion and ease of deposition [2].  Other materials considered were silicon monoxide, silicon dioxide and tantalum pentoxide.  Silicon monoxide and silicon dioxide were rejected because of their reactivity with chloride ions.  Tantalum pentoxide had been shown previously to be impervious to chloride corrosion [3], but the temperatures required for proper deposition would have complicated fabrication.  In this device, DC bias is set by the source through the resistance of the insulating layer (20-40 MΩ) [2].

The necessity of an ultra-low noise amplifier is particular to EEG recording. Unlike ECG, which is measured in mV, EEG is measured in μV, orders of magnitude smaller. This poses a problem related to our preference for high amplifier input impedance. To satisfy this requirement, the input stage was designed using metal-oxide-semiconductor FETs (MOSFETs). However, with this type of transistor, given the low-level signals of EEG, one needs to carefully manage noise from the amplifier, in particular flicker or 1/f noise.

1/f noise is so-named because its associated power spectral density (PSD) is inversely proportional to frequency. In MOSFETs, 1/f noise is attributed to the random trapping and detrapping of charge carriers in oxide defects at or near the semiconductor-insulator interface [4,5]. This trapping-detrapping process alters the channel carrier density. In addition, the trapped charges act as Coulombic scattering sites, inducing fluctuations into the channel mobility. Consideration of these two factors has been shown to accurately model 1/f noise in standard MOSFET transistors.

There are a number of ways to deal with this type of noise. The brute force approach is to create MOSFETs which by design have sufficiently low 1/f noise. MOSFETs are typically operated in saturation [6] for which the 1/f input referred noise is well-described by [5]

S Vg q 2 C ox 2 N ot WL 1 f MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4uamaaBaaaleaacaWGwbGaam4zaaqabaGccqGHfjcqdaWcaaqaaiaadghadaahaaWcbeqaaiaaikdaaaaakeaacaWGdbWaa0baaSqaaiaad+gacaWG4baabaGaaGOmaaaaaaGcdaWcaaqaaiaad6eadaWgaaWcbaGaam4BaiaadshaaeqaaaGcbaGaam4vaiaadYeaaaWaaSaaaeaacaaIXaaabaGaamOzaaaaaaa@4602@ .

(1.1)

Here, q MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyCaaaa@36E3@  is the electron charge, C ox MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBaaaleaacaWGVbGaamiEaaqabaaaaa@38D2@  the gate oxide capacitance per unit area, and W MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4vaaaa@36C9@  and L MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitaaaa@36BE@  the width and length of the channel respectively. N ot MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOtamaaBaaaleaacaWGVbGaamiDaaqabaaaaa@38D9@  , the equivalent density of oxide traps, is defined by

N ot [c m 2 ]= kT N t (E) γ MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOtamaaBaaaleaacaWGVbGaamiDaaqabaGccaGGBbGaam4yaiaad2gadaahaaWcbeqaaiabgkHiTiaaikdaaaGccaGGDbGaeyypa0ZaaSaaaeaacaWGRbGaamivaiaad6eadaWgaaWcbaGaamiDaaqabaGccaGGOaGaamyraiaacMcaaeaacqaHZoWzaaaaaa@4707@

(1.2)

where N t (E)[c m 3 e V 1 ] MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOtamaaBaaaleaacaWG0baabeaakiaacIcacaWGfbGaaiykaiaacUfacaWGJbGaamyBamaaCaaaleqabaGaeyOeI0IaaG4maaaakiaadwgacaWGwbWaaWbaaSqabeaacqGHsislcaaIXaaaaOGaaiyxaaaa@4330@  is the density of oxide traps per unit volume and unit energy, kT MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4Aaiaadsfaaaa@37B6@  is the Boltzmann constant times the temperature, and γ MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4SdCgaaa@3794@  is a parameter related to the effective mass of the tunneling carrier and the barrier height of the trap. (1.1) and (1.2) suggest three possibilities: (1) reduce the temperature, (2) select a process minimizing the density of oxide traps, and (3) maximize the width and length of the channel. Alizadeh-Taheri elected to implement (2) and (3), choosing p-doped MOS (PMOS) and fabricating channels with large dimensions [2]. It is well-established that the effective density of oxide traps in PMOS transistors is much lower than n-doped MOS (NMOS) transistors. As a result, S Vg MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4uamaaBaaaleaacaWGwbGaam4zaaqabaaaaa@38B8@  in PMOS devices can be several orders of magnitude lower than equivalent NMOS devices [2,5]. With regards to channel size, Alizadeh-Taheri set W=220 MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4vaiabg2da9iaaikdacaaIYaGaaGimaaaa@3A01@  mm and L=10 MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitaiabg2da9iaaigdacaaIWaaaaa@3939@  mm. For comparison, transistors in an Intel Pentium 4 processor have dimensions nearly a thousand times smaller, e.g., L=60 MathType@MTEF@5@5@+=feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitaiabg2da9iaaiAdacaaIWaaaaa@393E@  nm [7].

References
[1] B. Alizadeh-Taheri, R. L. Smith, and R. T. Knight, "An active, microfabricated, scalp electrode array for EEG recording," Sensors and Actuators A, vol. 54, pp. 606-611, 1996.

[2] B. Alizadeh-Taheri, "An Active Micromachined Scalp Electrode Array for EEG Signal Recording," Ph.D. dissertation, University of California Davis, Davis, CA 1994.

[3] C. H. Lagow, K. J. Sladek, and P. C. Richardson, "Anodic insulated tantalum oxide electrocardiograph electrodes," IEEE Trans Biomed Eng, vol. 18, no. 2, pp. 162-4, Mar 1971.

[4] K. K. Hung, P. K. Ko, C. Hu, and Y. C. Cheng, "A unified model for the flicker noise in metal-oxide-semiconductor field-effect transistors," IEEE Transactions on Electron Devices, vol. 37, no. 3, pt.1, pp. 654-65, 1990.

[5] Y. Nemirovsky, I. Brouk, and C. G. Jakobson, "1/f noise in CMOS transistors for analog applications," IEEE Transactions on Electron Devices, vol. 48, no. 5, pp. 921-7, 2001.

[6] B. Razavi, Design of analog CMOS integrated circuits. Boston, MA: McGraw-Hill, 2001.

[7] S. Thompson, M. Alavi, M. Hussein, P. Jacob, C. Kenyon, P. Moon, M. Prince, S. Sivakumar, S. Tyagi, and M. Bohr, "130nm Logic Technology Featuring 60nm Transistors, Low-K Dielectrics, and Cu Interconnects," Intel Technology Journal: Semiconductor Technology and Manufacturing, vol. 6, no. 2, pp. 1-13, 16 May 2002.

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August 18, 2003

God can change hearts

He can.

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August 15, 2003

Dissertation Instructions

I'm certainly not there yet - but in case I need it later (or you need it), here are the dissertation instructions. Scary.

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Oops - Recovering Files

I accidentally deleted a few GB's of something I really didn't want to delete from my AFS account. Fortunately, Stanford regularly backs up - and fortunately, I found instructions before they re-backed up. Whew.

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August 14, 2003

4 INT DEATH STAR - MAIN DOCKING BAY 4

The DEATH STAR COMMANDER, MOFF JERJERROD, a tall, confident technocrat, strides through the assembled troops to the base of the shuttle ramp. The troops snap to attention; many are uneasy about the new arrival. But the Death Star commander stands arrogantly tall.

The exit hatch of the shuttle opens with a WHOOSH, revealing only darkness. Then, heavy FOOTSTEPS AND MECHANICAL BREATHING. From this black void appears DARTH VADER, LORD OF THE SITH. Vader looks over the assemblage as he walks down the ramp.

JERJERROD
Lord Vader, this is an unexpected pleasure. We're honored by your presence.

VADER
You may dispense with the pleasantries, Commander. I'm here to put you back on schedule.

The commander turns ashen and begins to shake.

JERJERROD
I assure you, Lord Vader, my men are working as fast as they can.

VADER
Perhaps I can find new ways to motivate them.

JERJERROD
I tell you, this station will be operational as planned.

VADER
The Emperor does not share your optimistic appraisal of the situation.

JERJERROD
But he asks the impossible. I need more men.

VADER
Then perhaps you can tell him when he arrives.

JERJERROD (aghast)
The Emperor's coming here?

VADER
That is correct, Commander. And he is most displeased with your apparent lack of progress.

JERJERROD
We shall double our efforts.

VADER
I hope so, Commander, for your sake. The Emperor is not as forgiving as I am.

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August 12, 2003

More insight on EDL

The EDL is more complex than I ever imagined... in fact, all the existing models are deficient in some way. There are a number of possible mechanisms and the truth is probably a combination of everything. Since superposition works for potentials, we can break down the EDL into several sub-EDLs. A book I found (citation to come later) on this topic broke it up into ionic and electronic double layers. Let's start with the electronic double layer.

Electronic double layer
Imagine am uncharged conductor, say a piece of platinum. Electrons, being free, protrude a little bit outside the boundary of the ions. The classical way of thinking about this is that the electrons are kept from flying out by the positively-charged ions, but they have some room to go a bit further. The quantum mechanical way to think about this is that with any finite barrier, the probability density leaks out, decaying exponentially. Either way, electrons exist a bit outside the boundaries of the conductor. This exterior cloud of electrons forms one layer of the the double layer. The positive ions left behind form another. Now, outside the electron cloud no charge is seen, since the net charge of the conductor is 0. Remember that the surface integral of the electric field flux is equal to the net charge enclosed. So, this clarifies an earlier question I had. If you plunk down a non-reactive conductor into a liquid you will not cause an ionic layer to form around the conductor. This can only happen if the conductor is charged.

Ionic double layer
The ionic double layer forms when the electrode has extra charge, in which case, ions outside the electrode in the electrolyte redistribute themselves (statistically). Ions with charge opposite the charge of the electrode will have a greater concentration by the electrode, while ions with the same charge will have a smaller concentration. How can the electrode have extra charge? Here's where it gets a bit complex. If the electrode is polarizable, meaning that there are no reactions, then the only way to give extra charge is to do something like charging it up with a battery. If the electrode is non-polarizable, it can become charged up because a chemical reaction at the interface contributes or consumes an electron. Reactions which are energetically favorable will occur, leaving the electrode charged, and an EDL.

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Electric double layer II

Getting warmer, I found some good sounding articles:

Polarization of the electrical double layer. Time evolution after application of an electric field
Shilov, VN; Delgado, AV; Gonzalez-Caballero, E; Horno, J; Lopez-Garcia, JJ; Grosse, C
Source: JOURNAL OF COLLOID AND INTERFACE SCIENCE; DEC 1 2000; v.232, no.1, p.141-148

Dynamics of the electric double layer: Analysis in the frequency and time domains
Lopez-Garcia, JJ; Horno, J; Gonzalez-Caballero, F; Grosse, C; Delgado, AV
Source: JOURNAL OF COLLOID AND INTERFACE SCIENCE; AUG 1 2000; v.228, no.1, p.95-104

Will track them down tomorrow... its in the chemistry library.

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August 11, 2003

Electric double layer

The electric double layer or EDL occurs at the interface between electrolytes such as salt water and electrodes such as gold. How does this happen? Does it happen just between metals and electrolytes? Understanding this is crucial to addressing the swtich from a non-polarized electrode to a polarized electrode. I should have been documenting resources as I found them but I suppose it isn't too late to start. A good start, with pictures, can be found here. Ahh, and Daniel Laser at Stanford might know something....

It seems that quite a few resources, like the ones above, talk about the EDL forming because of some sort of oxidation or reduction reaction (even without current). However, I'm interested in seeing if an EDL forms without any such reaction, like in platinum. What happens if there is no reaction, is there EDL? What if the electrode is coated with an insulating material? What if the material is non-polarizable (is that really possible)? Help!

EDL and Microfluidics - Electroosmosis
I looked at bit closer at Daniel Laser's page and realized that it was about microfluidics. This also sort of answers my question about insulators and the double layer. In this case silicon oxide makes contact with water. A reaction occurs at the surface, which makes H+ and adds electrons to the surface of the silicon oxide. A double layer forms as a result. The focus here is not the EDL but the H+ ions that are formed. When a potential is applied across the channel, the H+ ions are pulled towards the cathode (or is it the anode - ugh!) which in turns drags everything else. I found more details here. This still doesn't answer the question I had about platinum, which does not react, but it does suggest that having an insulating layer is no good if it isn't something that won't react as well.

Ahh, something interesting. In this article about electroosmosis, it states that "most surfaces spontaneously develop an electric double layer when brought into contact with either weak or strong electrolyte solutions. This charge generation is caused by electrochemical reactions at the liquid/solid interface..." Ok, so hat if there is no reaction, like platinum, or stainless steel? Is there still an EDL without applied voltage? The reference for that statement is Hunter's "Zeta Potential in Colliod Science".

EDL and AFM
EDL has recently been used to improve atomic force microscopy (AFM). For those of you that are unfamiliar with the technique, AFM basically involves a micromachined cantilever with a very sharp tip jutting out at the end. As the cantilever is dragged across the surface it basically traces out the atoms on the surface allowing to you to see the topography of the surface. How does this relate to the EDL? I found this article by Sokolov et al. One of the problems in AFM is the attractive van der Waals force between the tip and the sample. Sokolov et al. propose using an EDL to shield some of the van der Waals forces.

The answer?
I looked up "electric double layer" and "platinum" on Google, and voila, I found what I was looking for... I think. I found an article from korea about an EDL-based battery which I had skipped over ealier. A polarizable electrode made of carbon is used. In figure 2, it shows the battery under discharged and charged conditions. Clearly, when the battery is discharged there is no double layer, but when the battery is charged there is. Nicely, this gives a good review of all the different double layer models AND uses a polarizable electrode. Still it isn't exactly what I'm looking for but the references will be of great value.

The problem.
This is what it says in Webster's book.

When a polarizable electrode is in contact with an electrolyte, space charge forms in two layers at the interface to produce the half-cell potential and a capacitive reactance for current flow. If the electrode is moved so that the space charge distribution is altered, then there is momentary change of the half-cell potential until equilibrium is reestablished. If
an electrode pair is in an electrolyte and one moves with respect to the other, a potential difference appears between the two electrodes during this movement. This potential is a motion artifact associated with a polarizable electrode and can be a serious interference source in recording biopotentials. From the equivalent circuit, there are two potential sources of motion artifact: Ehe and Ese. To minimize these effects, the polarizability of the electrode-skin interface must be reduced. The best way to do this is to insure good contact between the electrode and the inner layers of the epidermis, meaning that something must e done to the skin surface (i.e., abrasion) to minimize polarization [1].
What is this half-cell potential Neuman is talking about? If there is no oxidation or reaction, then where does this come from? Oh man, I'm getting tired.

Reference
[1] M. R. Neuman, "Biopotential Electrodes," in Medical instrumentation : application and design, J. G. Webster and J. W. Clark, Eds., 3rd ed. New York: Wiley, 1998, pp. 183-232.

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Sound card too fast?

Sometime ago, after installing and uninstalling a fancy audio card (that did not really work), I noticed that my computer was playing sound substantially faster - so much so that vocal recordings resembled the Chipmunks. It took me quite a while to sort out the problem but I finally found a very helpful thread in Google groups. If you have Intel AC'97 audio like I do, the solution, per David Hollway's post, is as follows:

  1. Update Intel chipset
  2. Update the audio driver by clicking Control Panel->System->Hardware->Device Manager->Sound, video and game controllers->AC'97 Audio codec->Driver->Update->Windows Update
It will offer to install SoundMax - that'll work.

Posted by torque at 5:03 PM | Comments (4) | TrackBack

August 9, 2003

Measuring voltage without current

Fundamentally, what are we measuring when we measure voltage? I think that we are really measuring the difference in how charge is perceived by two particular points. Actually, we are only taking the normal, the normal being parallel to the connection.

In the shower today I was thinking about balloons, static and hair. When you charge up a balloon by rubbing it in your hair, you create a potential between the balloon and yourself. More than that, the balloon really is charged up more than everything around. By bringing yourself close to the balloon, your hair gets attracted to the balloon so much so that it physically moves. Now, who does the work, is it the balloon? It's not, it is you, because it will take more work for you to approach the balloon since you must also force your hair to move. Why am I saying all this?

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Jerry Colonna

jcport2.jpg

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August 8, 2003

Donating a piece of yourself

I was able to give some platelets and plasma today at the Stanford Blood Center. The procedure took a little more than an hour, but it got me thinking about other things that I could donate, and not suffer too much for. I ended up signing up and donating some blood for typing to the National Marrow Donor Program. Although the chance of a match is quite small, this sort of thing really makes a difference. They now have a couple ways of getting the blood stem cells (what they really want) from the body. The old way is to stick a rather large needle into your femur and extract the marrow. The new way is to chemically force out the stem cells from your bones and extract the cells using apheresis. Blood stem cells are what produce blood cells in your body. Some people don't have this or have limited capacity - as you can imagine, it is a pretty bad scene... so if you can, give some blood and think about donating blood stem cells.

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More electrochemistry

"In any practical measurement of potentials, current flows in the measuring circuit for at least a fraction of the period of time over which the measurement is made. Ideally this current should be very small. However, in practical situations, it is never zero. Biopotential electrodes must therefore have the capability of conducting a current across the interface between the body and the electronic measuring circuit." - Michael Neuman in Medical Instrumentation [1]
This is the case if the current which flows is used to measure the potential, for instance through a resistor. What if the potential is all that we are after? Do we need to still worry about facilitating this current? Is the potential meaningful without current flow? Or, can we measure potential without current flow?

We can accelerate electrons in vacuum from one metal plate to another by imposing a voltage across the two plates. In most instances of this experiment, the electrons are released from one of the plates, so current really is flowing. Assuming that it is possible to drop an electron into the the field, would it accelerate? It would, so based on the acceleration we could measure the potential across the plates. Perhaps an even simpler experiment would be to send an accelerated electron through a perpendicular field and use the deflection to measure the strength of the field. So, it is possible to measure potential without current.

Now if we think about it, there is some wierdness going on. Where does the energy come from to create this field which does real work on the electron? Isn't that strange? If this was the case we could deflect electrons all day long for free. I'm not understanding something here...

Reference
[1] M. R. Neuman, "Biopotential Electrodes," in Medical instrumentation : application and design, J. G. Webster and J. W. Clark, Eds., 3rd ed. New York: Wiley, 1998, pp. 183-232.

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August 7, 2003

Transitioning from POP3 to IMAP

After using POP3-based Pine for so many years, I've recently decided to use IMAP, mostly because Stanford gives an extra 100 MB in space which I'd like to free up to do stuff like my blog. So, I started using IMAP-configured Outlook Express to access my mail. Fine, but all my old mail and addresses were still stored in Pine folders on Leland. Now what? The first step is to force Pine to use IMAP instead of downloading mail. Stanford has a pretty good document here which explains how to do it.

  1. First, disable automatic downloading using
    epic14:~> unsetenv LELAND_ENV
  2. Now, edit .pinerc using the editor of your choice, changing these lines
    inbox-path=
    folder-collections=Mail/[]
    To these lines
    inbox-path={torque.pobox.stanford.edu}INBOX
    folder-collections={torque.pobox.stanford.edu}INBOX.[], Mail/[]
    (Of course, you changed torque to your own username right?)
  3. Get a Kerberos 5 ticket using
    epic14:~> kinit -t
    Stanford University (Leland) (epic14.Stanford.EDU)
    Password for torque@stanford.edu:
  4. Now, if you start up Pine, it will access your IMAP folders directly. The last step is to move the old Pine folders you want to IMAP... and I don't know how to do that!
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The tale of two electrodes

I got stuck thinking-writing about wet electrodes. It's time to nail things down... which has been a bit fuzzy. The question is, how does one measure changes in potential on the scalp surface which result from some kind of electrical activity beneath the scalp. In tissue - in liquids - the movement of charge occurs via ionic currents. So, the goal is to take those ionic currents and to convert them to electrical currents to do our measurements. Another related question is what exactly causes these ionic currents? If it is an electrical field perhaps that is what we should measure, rather than the ionic current.

The textbook response is that there are two ways of doing this, using a non-polarizable electrode, or using a polarizable electrode. In the case of a non-polarizable electrode, oxidation or reduction reactions occuring at the electrode-electrolyte junction create or absorb free electrons. These reactions can either occur from the electrode or from the electrolyte. This type of electrode is modeled using a resistor, since real current flows. A polarizable electrode is one in which no oxidation or reduction reactions occur. Changes in ionic concentration at the electrode-electrolyte junction cause changes in electron concentration at the junction. In this case the measurement is based on displacement current. Typically noble metals such as platinum are used for this.

Ok, so given all this, what is actually happening? I thought about this on the way to Ranch 99 and it still puzzles me. Because of the underlying electrochemical reactions in the brain, a fluctuating field is built up. This field causes ions to move around (which also affect the field in someway). Now, at the surface of the scalp, we see some of this ion movement, and if we look at two locations, there may be a net charge difference, if there is, then there is a voltage between the two. By connecting the two locations using a wire, charge will flow... in some sense. If the connection is made using non-polarizable electrodes, then oxidation or reduction take place so that the charge build-up begins to be neutralized as electrons flow across the wire to neutralize the other side. If the connection is made using polarizable electrodes then effectively electrons in the wire bunch up to neutralize the positively charged side (and the other side). This current is measured using a galvanometer (for instance).

Now here's the interesting question, if it is some sort of potential that causes the ions to be in those locations in the first place, couldn't the same potential also cause current in the wire? You could imagine, for instance, some sort of cantilever with a fixed charge on one side and the scalp on the other. In this way you could measure fluctuations without a reference. Of course, it would be much more difficult to do differential measurements, but it could still be done. This is a way of measuring EEG in a completely different way.

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What is Man's Purpose?

Well, it's a new day again, and until midnight, there are 18, gloriously blank hours waiting to be filled. How will I fill them today? The Westminster Shorter Cathecism says that "Man's chief end is to glorify God and enjoy Him forever." So, my goal should be to fill those 18 hours with glorifying and enjoying God.

For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's.... Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God. -- 1 Corinthians 6:20, 31

07:45-07:59 Read the first entry in Training Hearts, Teaching Minds.
08:00-08:59 Breakfast with the family, went through the Passages of the Day.
09:00-09:14 Changed diaper, rushed teeth, washed face, got ready for the day!
09:15-09:34 Changed diaper (again), had vitamins with sweetie, washed dishes.
09:35-09:44 Took shuttle to library.
09:45-09:59 Got key for dissertation room...
10:00-12:59 Tried to write, struggled with electrochemistry
13:00-13:29 Fixed my Pine mailbox
13:30-14:29 Went home for lunch with sweetie and Linus
14:30-15:59 Shopped for food at Ranch 99
16:00-17:59 More electrochemistry at library, some database stuff
18:00-19:14 Dinner and clean-up
19:15-21:44 Fellowship
21:45-11:59 Shower, etc., talking with sweetie - ahhh where did the day go?

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August 6, 2003

Introduction to dry electrodes

Motivated principally by the need for stable long-term ECG at NASA, scientists have explored the possibility of dry electrodes since the early-60s. However, due of the ultra-low voltages involved, it was not until the mid-90s that Alizadeh-Taheri, et al. first published on a dry EEG sensor [1]. More recently, Harland et al. presented an alternate design based on commercially-available amplifiers [2]. In the following section, I detail important insights gained over the development of dry ECG sensors as well as the transition from dry ECG to dry EEG sensors.

Credit for the original dry electrode belongs to Lopez and Richardson [3]. Built in the late-60s, their insulated electrode was the first not to rely on an electrolytic solution for electrical contact with the body. Subsequent dry sensors, including the ones I have cited for EEG, have been based on it. This is not to say that there were not efforts prior the insulated electrode to record ECG or EEG without electrolytic paste. However, these early attempts were discouraging, the resulting recordings being severely hampered by motion artifacts. Lopez and Richardson addressed this issue by coupling surface potential fluctuations to the amplifier using a capacitive rather than resistive connection [4]. The electrode is called insulated because in this scenario the body is insulated from the amplifier. To appreciate this insight, we can skip back number of years to lithium chloride (LiCl) impregnated balsa wood electrodes.

References
[1] B. Alizadeh-Taheri, R. L. Smith, and R. T. Knight, "An active, microfabricated, scalp electrode array for EEG recording," Sensors and Actuators A, vol. 54, pp. 606-611, 1996.
[2] C. J. Harland, T. D. Clark, and R. J. Prance, "Remote detection of human electroencephalograms using ultrahigh input impedance electric potential sensors," Applied Physics Letters, vol. 81, no. 17, pp. 3284-3286, 2002.
[3] A. Lopez, Jr. and P. C. Richardson, "Capacitive electrocardiographic and bioelectric electrodes," IEEE Trans Biomed Eng, vol. BME-16, no. 1, p. 99, 1969.
[4] P. C. Richardson, F. K. Coombs, and R. M. Adams, "Some new electrode techniques for long-term physiologic monitoring," Aerosp Med, vol. 39, no. 7, pp. 745-50., 1968.

Posted by torque at 12:33 PM | Comments (125) | TrackBack

August 2, 2003

UPC lookup

I was just thinking about this the other day, and my goodness, someone actually has done it! Imagine, a UPC based marketplace. The amazing thing is, you can actually download the database from sourceforge! Imagine that. Unbelieveable.

Posted by torque at 9:46 PM | Comments (0) | TrackBack

August 1, 2003

At it again

I bet you are thinking, boy, he's at it again. I installed PHP/Apache/MySQL on the laptop today. Some important things. First, after installing PHP, install Apache and make the following additions to the httpd.conf file:

LoadModule php4_module "C:/Program Files/php/sapi/php4apache2.dll"
AddType application/x-httpd-php .php

And then edit the line
DirectoryIndex index.php index.html index.html.var

Posted by torque at 2:48 PM | Comments (0) | TrackBack